1. Field of the Invention
The present invention relates to a disposable pressure transducer apparatus for use in blood pressure measurement, and in particular, to such an apparatus comprising a semiconductor pressure transducer element or a semiconductor pressure sensor hydraulically coupled to a housing passageway and a temperature compensating circuit connected to the semiconductor pressure sensor.
2. Description of the Prior Art
In the pressure transducer apparatus, the semiconductor pressure sensor converts blood pressure pulses transmitted through a fluid in a catheter inserted into a blood vessel into an electric signal. The electric signal is temperature compensated by the temperature compensating circuit and is transmitted to a monitoring device which displays the blood pressure.
A known apparatus of a type described above comprises a housing having an interior and a wall portion formed with the housing passageway to be coupled with the catheter. The semiconductor pressure sensor and an electric circuit including the temperature compensating circuit are mounted on a first surface of a dielectric substrate. The substrate has an opposite or second surface which is secured onto an inner surface of the wall portion. The semiconductor pressure sensor is hydraulically coupled with the housing passageway through the wall portion. The electric circuit is connected to the semiconductor pressure sensor and electric conductors electrically connect the electric circuit to the monitoring device. The known apparatus is disclosed in U.S. Pat. No. 4,576,181 issued to Wallace et al and assigned to Utah Medical Products (Reference I).
Since the semiconductor pressure sensor and the electric circuit including the temperature compensating circuit are formed on the same first surface of the substrate together with an opaque cap or a chip cover for the sensor in the known apparatus, manufacture and assembly of the apparatus are greatly facilitated as described in Reference I.
However, in the known apparatus the temperature compensation is not very good because the temperature compensating circuit is disposed on the first surface of the substrate away from the wall portion having the passageway and is remote from the fluid introduced into the passageway.
The temperature compensating circuit is usually formed on the substrate by a thick printing technique. That is, resistor and conductor patterns are formed by the printing method. The resistors are trimmed by a laser working technique to adjust the resistances. Evaporation and/or dust of the resistors is generated in the laser trimming process and contaminates an outer surface of the semiconductor pressure sensor mounted on the same surface of the substrate. This is not avoided by provision of the chip cover because the chip cover is provided with an aperture for communicating the semiconductor pressure sensor with the atmosphere. As a result, the semiconductor pressure sensor is deteriorated in reliability so that the apparatus has a problem in manufacturing yield and reliability of operation.
In order to form the electric circuit including the temperature compensating circuit on the same surface of the substrate on which the semiconductor pressure sensor is mounted together with the chip cover, the substrate is required comparatively large in size. This unfortunately results into a large size of the apparatus.